1. Field of the Invention
The present invention relates to a method, system, and program for discovering devices communicating through a switch.
2. Description of the Related Art
A storage area network (SAN) comprises a network linking one or more servers to one or more storage systems. Each storage system could comprise a Redundant Array of Independent Disks (RAID) array, tape backup, tape library, CD-ROM library, or JBOD (Just a Bunch of Disks) components. One common protocol for enabling communication among the various SAN devices is the Fibre Channel protocol, which uses optical fibers or copper wires to connect devices and provide high bandwidth communication between the devices. In Fibre Channel terms the “fabric” comprises one or more interconnected switches, such as cascading switches, that connect the devices. The link is the two unidirectional fibers, which may comprise an optical wire, transmitting to opposite directions with their associated transmitter and receiver. Each fiber is attached to a transmitter of a port at one end and a receiver of another port at the other end.
The Fibre Channel protocol defines a fabric topology. A fabric includes one or more interconnected switches, each switch having multiple ports, also referred to as F—Ports. A fiber link may connect an N—Port, or node port, on a device to one F—Port on the switch. An N—Port refers to any port on a non-switch device. An N—Port can communicate with all other N—Ports attached to the fabric to which the N—Port is connected, i.e., N—Ports on the immediate switch or interconnected cascading switches.
Another common Fibre Channel topology is the arbitrated loop. The devices in an arbitrated loop are daisy chained together. An L—Port is a port on a device that has arbitrated loop capabilities. An NL—Port is a device port that is part of a loop and capable of communicating with other N—Ports in a fabric. An FL—Port is a switch port connected to a loop. In a private loop In a public loop topology, a switch FL—Port is connected to the arbitrated loop, thereby allowing communication between the fabric devices and the loop devices. However, often legacy private loop devices are unable to communicate on a fabric because the private loop devices utilize an eight bit Arbitrated Loop Physical Address (AL—PA), and do not have the 24 bit address that is used for communication on the fabric.
To migrate legacy private loop devices that are only capable of using the eight bit AL—PA to a switched fabric, Q Logic Corporation provides the SANbox-16STD Fibre Channel switch that incorporates multiple private loop devices into a switched fabric. The QLogic switch includes multiple Segmented Loop Ports (SL—Ports), which function as FL—Ports and may have an attached private loop, also referred to as a looplet. Thus, the QLogic switch is comprised of multiple SL—Ports, where each SL port may support a separate arbitrated loop that has attached private loop devices. The SL ports on the switch and any devices attached to looplets attached to the SL—Ports are configured as a single logical Fibre Channel Arbitrated Loop (FC-AL), also referred to as a segmented loop. During initialization, the switch assigns unique eight bit Arbitrated Loop Physical Addresses (AL—PAs) to each SL—Port and to any device attached to a looplet on an SL—Port to form a segmented loop. Within a segmented loop any device within one private looplet attached to one SL—Port may communicate with any device in another private looplet attached to another SL port on the switch. Further details of the SANbox-16STD Fibre Channel switch are described in the QLogic publications “SANbox-16STD Fibre Channel Switch: Installer's/User's Manual,” QLogic Publication No. 59012-03 Rev. A (August, 2000) and “Reducing the Complexity of Managing Private Loops”, a White Paper (2000), downloaded from the Internet at “http://www.qlogic.com/products/pdf/private—loops.pdf”, which publications are incorporated herein by reference in their entirety.
In such segmented loop environments, a systems administrator may want to understand and visualize the topology of all the devices on the segmented loop, such as the relationship of devices in looplets attached to SL—Ports on a switch, including devices in the same zone as well as other zones. Thus, there is a need in the art for improved techniques for ascertaining the topology of an arrangement of private loops attached to a switch.